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1. Field of the Invention
The present invention relates to a metering device.
2. Background of the Invention
Metering devices have been proposed before. One type of metering device is used to control the dispensing of a liquid or fluid, which may be supplied to the metering device under pressure, and the metering device acts to dispense a precisely predetermined quantity of the liquid or fluid. An alternative form of metering device monitors the flow rate of liquid or fluid passing through the device.
The present invention seeks to provide a metering device which may be used for either of the purposes outlined above.
It is to be noted that it has been proposed previously to use metering devices to control the relative metering of two or more reactive liquids which together form a two-component reactive system in ratio to each other prior to their being mixed and dispensed. Examples of such two-component reactive systems are epoxies, polyurethanes, acrylics, silicones and polysulphides with their typical functions as sealing, bonding, encapsulating, coating, mould making, moulding and electrical or thermal insulating. Needless to say, such materials are currently used in nearly every type of production circumstance and across a very broad range of industries.
Despite their current importance and level of application, it should be appreciated that the use of multi-component reactive liquid systems, despite all the advantages, is still the subject of considerable scepticism by designers and production engineers. This is for the simple reason that xe2x80x9cstate of the artxe2x80x9dshot or flow metering, mixing and dispensing machinery does not assure that the correct relative proportioning of the two or more chemical components takes place within a tolerance, or even that it takes place at all. Mixed resin color changes, such as yellow and blue mixing to become green, can sometimes be used for visually checking that a degree of correct proportioning has taken place, but many premixed components are of approximately the same color and therefore no change is identifiable visually. Also, mixed product testing can be done on a random basis but if it is, it is not a check on the total product. Therefore, with the fact that xe2x80x9cstate of the artxe2x80x9dmachines can, and do, partially fail, fluctuate in failure, progressively fail through wear or totally fail, this is an area where the end mixed product specification is unqualified and where part or total failure of the end product remains a hazard. The scepticism of production engineers concerning this type of process is understandable, especially since quality assurance standards demand total control. Only sectors of the aircraft industry can presently justify a costly one hundred percent quality assurance system whereby part of a product batch is applied to a structure with its position in a structure being recorded while the other part of the batch is laboratory tested, rejected or approved, documented and stored.
While two or more component reactive systems have been mentioned, there are other areas of great significance where metering takes place such as with multiple chemical stream processes or in a single component metered shot application as, for instance, with grease being placed within a bearing. In all applications, the need remains to assure performance but in some applications the need is to ensure the avoidance of a catastrophe through product failure in the field.
EP 0,646,776A discloses a metering device for fluids which is specifically intended for use in a proportioning and mixing apparatus for a two-component material. The device is an oscillatory device.
In the arrangement disclosed in EP 0,646,776A, a housing is provided having a fluid inlet and a fluid outlet. A passage, within the housing, forms a communication between the fluid inlet and the fluid outlet. A rotary member is provided located within the passage which effectively seals the passage, the rotary member defining a diametrically extending bore which, in two rotational positions of the rotary member, becomes aligned with the passage. A ball is contained within the bore, and is adapted to form a sealing engagement with each of two seats provided for that purpose, at opposed ends of the bore.
In use of the metering device, shown in EP 0,646,776A, after the apparatus has been primed, so that the flow passage Within the housing and the bore within the rotary member are both full of liquid to be dispensed, when the rotary member is moved to a first position, with the ball engaging the seat located closest to the fluid inlet, fluid will flow through the fluid inlet and into the bore, pushing the ball away from the seat so that the ball moves axially of the bore until the ball engages the other seat. Fluid that was initially contained with the bore is thus expelled into the part of the passage adjacent the fluid outlet so that fluid is forced out of the metering device. When the ball engages the seat which is located adjacent the fluid outlet, no further fluid can flow through the device.
The rotatable element is then rotated through 180xc2x0 so that the ball is again located at a position adjacent the fluid inlet. The cycle of operation then repeats. The rotatable element is rotated at such a rate that it is anticipated that the ball completes the journey from one seat to the other seat on every occasion that the rotatable element is in a position such that the bore is aligned with the passageway.
It is often difficult to maintain appropriate seals in the arrangement disclosed in EP 0,646,776A, bearing in mind that the ball is subjected permanently to the source of the fluid under pressure.
The present invention seeks to provide an improved metering device.
According to this invention there is provided a metering device, the metering device comprising means defining a chamber having two opposed ends comprising an elongate bore, each end of the elongate bore accommodating a respective probe, the inner ends of which bound the chamber, at least one probe being axially adjustable in position, each probe having electrically conductive means extending from the inner end face of the probe, there being inlet means to enable fluid to enter one end of the chamber and inlet means to enable fluid to enter the other end of the chamber, there being outlet means to enable fluid to exit from said one end of the chamber, and outlet means to enable fluid to exit from the other end of the chamber, there being a shuttle provided within the chamber at a position intermediate said two ends, at least the opposed ends of the shuttle being electrically conductive, the shuttle acting sealingly to separate the two ends of the chamber, the shuttle being movable between two terminal positions, each probe being responsive to physical contact with the shuttle to generate a respective electrical signal when the shuttle reaches each one of said two terminal positions, there being valve means to control fluid flow which, in one condition, permit the entry of fluid into one end of the chamber and permit the simultaneous exit of fluid from the other end of the chamber and which, in another condition, permit the entry of the fluid into said other end of the chamber and permit simultaneous exit of fluid from the said one end of the chamber, there being control means adapted to change the condition of the valve means on receipt of a said electric signal generated when the shuttle reaches a said terminal position.
Advantageously the inlet and outlet means incorporate ports in the side-wall of the chamber and the inner-most end of each probe which defines the chamber is configured to permit the entry or exit of fluid if the inner-most end of the probe is aligned with a said port.
Conveniently the inner-most ends of the probes which defines the chamber are of reduced diameter.
Preferably the shuttle has a central part which is a sealing sliding fit within the chamber, and two terminal end parts of reduced diameter.
Preferably the valve means is constituted by a rotor assembly, the rotor assembly being such that in one position thereof a fluid flow is established between a first inlet, and one end of the chamber, and is also established between the other end of the chamber and a first outlet, whereas in a second position of the rotor assembly fluid flow is established between a second inlet and the other end of the chamber, and between said one end of the chamber mid a second outlet, the rotor assembly being movable, by motor means, between said positions in response to a signal generated when the shuttle reaches one of said terminal positions.
Advantageously, the device comprises a housing provided with first inlet means and second inlet means, and also provided with first outlet means and second outlet means, the rotor assembly being rotatable within the housing, the motor assembly having an element defining the said chamber, and also defining a first passage which extends from one end of the chamber and a second passage which extends from the other end of the chamber, the rotor assembly, in one position, having the first passage aligned with and in communication with said first inlet and said second passage aligned with and in communication with said first outlet, and being rotatable to a second position in which said first passage is aligned with and in communication with said second outlet and said second passage is in alignment with and in communication with said second inlet the said passages being substantially sealed in other positions of the rotor.
Conveniently the rotor has a first plurality of passages located to be aligned individually, on rotation of the rotor, with the first inlet and second outlet, and a second plurality of passages located to be aligned individually, on rotation of the rotor, with the second inlet and first outlet.
Preferably said first plurality of passages and said second plurality of passages each comprise an odd number of passages, between five and nine.
Conveniently the rotor assembly has a body portion, the body having a central region with a relatively large diameter, the body tapering, from the central region of large diameter, towards opposed ends of the body, each tapering part of the body being snugly received within a co-operating frusto-conical or tapering opening formed in a respective annular element, each annular element being provided with a respective said inlet and a respective said outlet.
Preferably said annular elements are retained within a housing, and means are provided to apply force to the annular elements to bias the elements inwardly into secure sealing contact with the tapering parts of the body.
Conveniently the force applying means comprise means to apply hydraulic pressure to the end faces of the annular elements.
In an, alternative preferred embodiment of the invention the metering device comprises a fixed body, the fixed body defining said chamber and defining first inlet means, second inlet means, first outlet means and second outlet means, each of said inlet means and outlet means terminating at an exterior surface of the body at a position adjacent the termination, at the exterior of the body, of a respective passage leading to a respective end of the said chamber, the rotor assembly being mounted on the exterior of the body, the rotor assembly having means which, in one position of the rotor assembly, create a communication between the first inlet and the respective passage, and the second outlet and the respective passage and which, in an alternate position of the rotor assembly establish a connection between the second inlet and the respective passage, and the first outlet and the respective passage but which, in other positions of the rotor assembly, substantially seal said inlets and said passages.
In a further embodiment the valve mean comprise individual valves associated with said inlet means and outlet means.
In one arrangement one end of the chamber is connected to a valve, the valve being adapted to connect said one end of the chamber selectively to either a source of fluid to be introduced to the chamber, or to an exit conduit, the other end of the chamber being connected to a second corresponding valve adapted to connect the said other end of the chamber selectively to either an exit conduit, or a source of fluid to be introduced to the chamber.
In another arrangement each end of the chamber is associated with a respective entry conduit and exit conduit, each conduit having a respective valve to control flow in the conduit.
Preferably a sensor is provided to sense fluid leaking from the device and to generate a signal indicative of the fluid leakage detected.
Conveniently the device further incorporates stop valve means in a flow path for fluid leaving the chamber, the stop valve means being adapted to be opened only when the valve means permit flow from the chamber to the flow path.
The invention also relates to a metering device arrangement which incorporates two metering devices as described above, each metering device being associated with a reservoir of liquid to be metered by the metering device, the outlets of the metering devices being directed to a mixer adapted to mix liquids from the reservoirs when metered by the devices, the control means of the metering devices each providing signals to a supervising control arrangement, the supervising control arrangement being adapted to stop the operation of one metering device in response to a ceasing of the operation of the other metering device.
Preferably the control means of each metering device pass a signal to the supervising control means on receipt of a signal generated when a shuttle of the respective metering device reaches a respective terminal position, the supervising control means incorporating counters adapted to count the signals, and means to compare the counts present in the counter, the supervising control further including means adapted to stop operation of the metering devices if an output from the comparator exceeds a predetermined threshold.
Advantageously means are provided to re-set the counters when the count in a counter exceeds a predetermined threshold.